Technique to avoid cascaded hot spotting

ABSTRACT

The present invention overcomes the disadvantages of the prior art by providing a technique that stripes data containers across volumes of a striped volume set (SVS) using one of a plurality of different data placement patterns to thereby reduce the possibility of hotspots arising due to each data container using the same data placement pattern within the SVS. The technique is illustratively implemented by calculating a first index value, an intermediate index value and calculating a hash value of an mode associated with a data container to be accessed within the SVS. A final index value is calculated by multiplying the intermediate index value by the hash value, modulo the number of volumes of the SVS. Further, a Locate( ) function may be used to compute the location of data container content in the SVS to which a data access request is directed to ensure consistency of such content.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of commonly assigned U.S.patent application Ser. No. 11/834,412, which was filed on Aug. 6, 2007now U.S. Pat. No. 7,975,102, by Robert Wyckoff Hyer Jr. for a TECHNIQUETO AVOID CASCADED HOT SPOTTING and is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to storage systems and, in particularto striping a data container across a plurality of volumes on one ormore storage systems.

2. Background Information

A storage system typically comprises one or more storage devices intowhich information may be entered, and from which information may beobtained, as desired. The storage system includes a storage operatingsystem that functionally organizes the system by, inter alia, invokingstorage operations in support of a storage service implemented by thesystem. The storage system may be implemented in accordance with avariety of storage architectures including, but not limited to, anetwork-attached storage (NAS) environment, a storage area network (SAN)and a disk assembly directly attached to a client or host computer. Thestorage devices are typically disk drives organized as a disk array,wherein the term “disk” commonly describes a self-contained rotatingmagnetic media storage device. The term disk in this context issynonymous with hard disk drive (HDD) or direct access storage device(DASD).

The storage operating system of the storage system may implement ahigh-level module, such as a file system, to logically organize theinformation stored on volumes as a hierarchical structure of datacontainers, such as files and logical units. For example, each “on-disk”file may be implemented as set of data structures, i.e., disk blocks,configured to store information, such as the actual data for the datacontainer. These data blocks are organized within a volume block number(vbn) space that is maintained by the file system. The file system mayalso assign each data block in the data container a corresponding “fileoffset” or file block number (fbn). The file system typically assignssequences of fbns on a per-file basis, whereas vbns are assigned over alarger volume address space. The file system organizes the data blockswithin the vbn space as a “logical volume”; each logical volume may be,although is not necessarily, associated with its own file system.

A known type of file system is a write-anywhere file system that doesnot overwrite data on disks. If a data block is retrieved (read) fromdisk into a memory of the storage system and “dirtied” (i.e., updated ormodified) with new data, the data block is thereafter stored (written)to a new location on disk to optimize write performance. Awrite-anywhere file system may initially assume an optimal layout suchthat the data is substantially contiguously arranged on disks. Theoptimal disk layout results in efficient access operations, particularlyfor sequential read operations, directed to the disks. An example of awrite-anywhere file system that is configured to operate on a storagesystem is the Write Anywhere File Layout (WAFL®) file system availablefrom Network Appliance, Inc., Sunnyvale, Calif.

The storage system may be further configured to operate according to aclient/server model of information delivery to thereby allow manyclients to access data containers stored on the system. In this model,the client may comprise an application, such as a database application,executing on a computer that “connects” to the storage system over acomputer network, such as a point-to-point link, shared local areanetwork (LAN), wide area network (WAN), or virtual private network (VPN)implemented over a public network such as the Internet. Each client mayrequest the services of the storage system by issuing file-based andblock-based protocol messages (in the form of packets) to the systemover the network.

A plurality of storage systems may be interconnected to provide astorage system environment or cluster configured to service manyclients. Each storage system or node may be configured to service one ormore volumes, wherein each volume stores one or more data containers. Inone embodiment the volumes serviced by the particular node may bedistributed among all of the nodes of the environment. This embodimentdistributes the data access requests, along with the processingresources needed to service such requests, among all of the nodes,thereby reducing the individual processing load on each node. In anotherembodiment, a data container may be striped across a plurality ofvolumes configured as a striped volume set (SVS), where each volume isserviced by a different node of the cluster, thereby distributing theload for the single data container among a plurality of node. Atechnique for data container striping is described U.S. Pat. No.7,698,289, entitled STORAGE SYSTEM ARCHITECTURE FOR STRIPING DATACONTAINER CONTENT ACROSS VOLUMES OF A CLUSTER, by Michael Kazar, et al,the contents of which are hereby incorporated by reference.

In the latter embodiment described above, each data container is stripedacross the plurality of volumes using an identical striping (i.e., dataplacement) pattern. That is, the same data placement pattern is used foreach of a plurality of data containers striped across the SVS. Thus, asdata is written to data containers, the volumes comprising the SVS aretraversed in the same order for each data container. A noteddisadvantage of such identical volume traversal arises when a pluralityof data containers have continued write operations directed to them. Insuch situations, one or more nodes servicing the volumes may becomeunnecessarily overloaded processing the contained write operations,thereby rendering one or more volumes of the SVS a “bottleneck.”Eventually, the increasingly bottlenecked volume of the SVS may become ahotspot. As used herein, a hotspot is a localized area to which asignificant number of data access requests are directed. Systemresources may become overloaded while attempting to process the dataaccess requests, resulting in a concomitant loss of throughput.Consequently, because identical striping patterns are used, as thecurrent “bottlenecked” volume completes its I/O (input/output)operations, each subsequent data container will receive the next set ofI/O operations directed to the next volume designated by the stripingalgorithm, thus becoming the new “bottlenecked” volume. In this way, awave of bottlenecks cascades among the volumes in accordance with thestriping algorithm.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages of the prior art byproviding a technique that stripes data containers across volumes of astriped volume set (SVS) using one of a plurality of different dataplacement patterns to thereby reduce the possibility of (cascading)hotspots arising due to each data container using the same dataplacement pattern within the SVS. Illustratively, the SVS is serviced bya storage system architecture that comprises a plurality of nodesinterconnected as a cluster. Notably, the novel technique enables morethan one data placement pattern to be used to stripe the data containersacross the volumes of the SVS, thus facilitating steady servicing ofdata access requests by the nodes and reducing the effects of hotspots.

Illustratively, the SVS is associated with a set of striping rules thatdefine a particular stripe algorithm, a stripe width and an ordered listof volumes within the SVS. The stripe algorithm specifies the manner inwhich data container content is apportioned as stripes across theplurality of volumes, while the stripe width specifies the size/width ofeach stripe. The ordered list of volumes specifies the function andimplementation of the various volumes and striping rules of the SVS. Forexample, the ordering of the volumes in the list may denote the mannerof implementing a particular data placement pattern.

Further, a Locate( ) function may be used to compute the location ofdata container content in the SVS to which a data access request isdirected to thereby ensure consistency of such content served by thecluster. Illustratively, the Locate( ) function accepts as an input anmode number of the data container and an offset value indicating anoffset into the data container. A first index value is determined byfirst adding the mode number to the value of the offset divided by thestripe width with the sum then taken modulo the striping table size.Next, an intermediate index value is generated by indexing the firstvalue into the ordered list of volumes. A hash value is then obtainedby, for example, indexing, using the mode number, into an arraycomprising values (numbers) that have been selected to be mutually primewith the size of an ordered list of volumes, which may comprise astriping table. The first index value may then be cached into aconfiguration table. A final value is determined by multiplying theintermediate index value by the hash value, modulo the number of volumesof the SVS. The final value is then used to identify and locate thevolume (and node servicing the volume) by indexing into the stripetable.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of invention may be better understoodby referring to the following description in conjunction with theaccompanying drawings in which like reference numerals indicateidentical or functionally similar elements:

FIG. 1 is a schematic block diagram of a plurality of nodesinterconnected as a cluster in accordance with an illustrativeembodiment of the present invention;

FIG. 2 is a schematic block diagram of a node in accordance with anillustrative embodiment of the present invention;

FIG. 3 is a schematic block diagram of a storage operating system thatmay be used on a node in accordance with an illustrative embodiment ofthe present invention;

FIG. 4 is a schematic block diagram illustrating the format of a clusterfabric (CF) message in accordance with an illustrative embodiment ofwith the present invention;

FIG. 5 is a schematic block diagram illustrating the format of a datacontainer handle in accordance with an illustrative embodiment of thepresent invention;

FIG. 6 is a schematic block diagram of an exemplary mode in accordancewith an illustrative embodiment of the present invention;

FIG. 7 is a schematic block diagram illustrating a collection ofmanagement processes in accordance with an illustrative embodiment ofthe present invention;

FIG. 8 is a schematic block diagram of a volume location database (VLDB)volume entry in accordance with an illustrative embodiment of thepresent invention;

FIG. 9 is a schematic block diagram of a VLDB aggregate entry inaccordance with an illustrative embodiment of the present invention;

FIG. 10 is a schematic block diagram of a VLDB SVS entry in accordancewith an illustrative embodiment the present invention;

FIG. 11 is a schematic block diagram illustrating the periodicsparseness of data container content stored on volumes of a SVS inaccordance with an illustrative embodiment of the present invention;

FIG. 12 is a flowchart detailing the steps of a procedure for processinga data access request directed to a data container striped in accordancewith an illustrative embodiment of the present invention; and

FIG. 13 is a flowchart detailing the steps of a procedure foridentifying a location of a volume containing desired data in accordancewith an illustrative embodiment of the present invention.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

The present invention overcomes the disadvantages of the prior art byproviding a technique that stripes data containers across volumes of astriped volume set (SVS) using one of a plurality of different dataplacement patterns to thereby reduce the possibility of hotspots arisingdue to each data container using the same data placement pattern withinthe SVS. The technique is illustratively implemented by calculating afirst index value, an intermediate index value and then calculating ahash value of an mode associated with a data container to be accessedwithin the SVS. A final index value is subsequently calculated bymultiplying the intermediate index value by the hash value, modulo thenumber of volumes of the SVS. Further, a Locate( ) function may be usedto compute the location of data container content in the SVS to which adata access request is directed to thereby ensure consistency of suchcontent.

A. Cluster Environment

FIG. 1 is a schematic block diagram of a plurality of nodes 200interconnected as a cluster 100 and configured to provide storageservice relating to the organization of information on storage devices.The nodes 200 comprise various functional components that cooperate toprovide a distributed storage system architecture of the cluster 100. Tothat end, each node 200 is generally organized as a network element(N-Module 310) and a disk element (D-Module 350). The N-Module 310includes functionality that enables the node 200 to connect to clients180 over a computer network 140, while each D-Module 350 connects to oneor more storage devices, such as disks 130 of a disk array 120. Thenodes 200 are interconnected by a cluster switching fabric 150 which, inthe illustrative embodiment, may be embodied as a Gigabit Ethernetswitch. An exemplary distributed file system architecture is generallydescribed in U.S. Patent Application Publication No. US 2002/0116593titled METHOD AND SYSTEM FOR RESPONDING TO FILE SYSTEM REQUESTS, by M.Kazar et al. published Aug. 22, 2002. It should be noted that whilethere is shown an equal number of N and D-Modules in the illustrativecluster 100, there may be differing numbers of N and/or D-Modules inaccordance with various embodiments of the present invention. Forexample, there may be a plurality of N-Modules and/or D-Modulesinterconnected in a cluster configuration 100 that does not reflect aone-to-one correspondence between the N and D-Modules. As such, thedescription of a node 200 comprising one N-Module and one D-Moduleshould be taken as illustrative only.

The clients 180 may be general-purpose computers configured to interactwith the node 200 in accordance with a client/server model ofinformation delivery. That is, each client may request the services ofthe node, and the node may return the results of the services requestedby the client, by exchanging packets over the network 140. The clientmay issue packets including file-based access protocols, such as theCommon Internet File System (CIFS) protocol or Network File System (NFS)protocol, over the Transmission Control Protocol/Internet Protocol(TCP/IP) when accessing information in the form of files anddirectories. Alternatively, the client may issue packets includingblock-based access protocols, such as the Small Computer SystemsInterface (SCSI) protocol encapsulated over TCP (iSCSI) and SCSIencapsulated over Fibre Channel (FCP), when accessing information in theform of blocks.

In previous striping systems, such as that described in above-referencedU.S. Pat. No. 7,698,289, data containers are striped using identicalalgorithms across volumes serviced by the D-Modules. In such systems, aplurality of clients may be accessing sections of data containers thatare serviced by a single D-Module. The single D-Module may becomeinundated with an overwhelming demand for data access requests. Onceoverloaded, the hotspot may cascade as each data container utilizes thesame striping technique. As a result, a concomitant loss of throughputmay occur and the hotspot may become exacerbated as more data accessoperations are received while the rate of data access completion remainsstagnant.

B. Storage System Node

FIG. 2 is a schematic block diagram of a node 200 that is illustrativelyembodied as a storage system comprising a plurality of processors 222a,b, a memory 224, a network adapter 225, a cluster access adapter 226,a storage adapter 228 and local storage 230 interconnected by a systembus 223. The local storage 230 comprises one or more storage devices,such as disks, utilized by the node to locally store configurationinformation (e.g., in configuration table 235) provided by one or moremanagement processes that execute as user mode applications 700 (seeFIG. 7). The cluster access adapter 226 comprises a plurality of portsadapted to couple the node 200 to other nodes of the cluster 100. In theillustrative embodiment, Ethernet is used as the clustering protocol andinterconnect media, although it will be apparent to those skilled in theart that other types of protocols and interconnects may be utilizedwithin the cluster architecture described herein. In alternateembodiments where the N-Modules and D-Modules are implemented onseparate storage systems or computers, the cluster access adapter 226 isutilized by the N/D-Module for communicating with other N/D-Modules inthe cluster 100.

Each node 200 is illustratively embodied as a dual processor storagesystem executing a storage operating system 300 that preferablyimplements a high-level module, such as a file system, to logicallyorganize the information as a hierarchical structure of named datacontainers, such as directories, files and special types of files calledvirtual disks (hereinafter generally “blocks”) on the disks. However, itwill be apparent to those of ordinary skill in the art that the node 200may alternatively comprise a single or more than two processor system.Illustratively, one processor 222 a executes the functions of theN-Module 310 on the node, while the other processor 222 b executes thefunctions of the D-Module 350.

The memory 224 illustratively comprises storage locations that areaddressable by the processors and adapters for storing software programcode and data structures associated with the present invention. Theprocessor and adapters may, in turn, comprise processing elements and/orlogic circuitry configured to execute the software code and manipulatethe data structures. The storage operating system 300, portions of whichis typically resident in memory and executed by the processing elements,functionally organizes the node 200 by, inter alia, invoking storageoperations in support of the storage service implemented by the node. Itwill be apparent to those skilled in the art that other processing andmemory means, including various computer readable media, may be used forstoring and executing program instructions pertaining to the inventiondescribed herein.

The network adapter 225 comprises a plurality of ports adapted to couplethe node 200 to one or more clients 180 over point-to-point links, widearea networks, virtual private networks implemented over a publicnetwork (Internet) or a shared local area network. The network adapter225 thus may comprise the mechanical, electrical and signaling circuitryneeded to connect the node to the network. Illustratively, the computernetwork 140 may be embodied as an Ethernet network or a Fibre Channel(FC) network. Each client 180 may communicate with the node over network140 by exchanging discrete frames or packets of data according topre-defined protocols, such as TCP/IP.

The storage adapter 228 cooperates with the storage operating system 300executing on the node 200 to access information requested by theclients. The information may be stored on any type of attached array ofwritable storage device media such as video tape, optical, DVD, magnetictape, bubble memory, electronic random access memory, micro-electromechanical and any other similar media adapted to store information,including data and parity information. However, as illustrativelydescribed herein, the information is preferably stored on the disks 130of array 120. The storage adapter comprises a plurality of ports havinginput/output (I/O) interface circuitry that couples to the disks over anI/O interconnect arrangement, such as a conventional high-performance,FC link topology.

Storage of information on each array 120 is preferably implemented asone or more storage “volumes” that comprise a collection of physicalstorage disks 130 cooperating to define an overall logical arrangementof volume block number (vbn) space on the volume(s). Each logical volumeis generally, although not necessarily, associated with its own filesystem. The disks within a logical volume/file system are typicallyorganized as one or more groups, wherein each group may be operated as aRedundant Array of Independent (or Inexpensive) Disks (RAID). Thevolumes may be embodied as flexible volumes and further organized as oneor more aggregates. Aggregates and flexible (virtual) volumes aredescribed in U.S. Pat. No. 7,409,494 titled EXTENSION OF WRITE ANYWHEREFILE SYSTEM LAYOUT, by John K. Edwards, et al, and assigned to NetworkAppliance, Inc., which is hereby incorporated by reference as thoughfully set forth herein.

As noted above, in previous striping systems, data containers may bestriped using identical algorithms across a volume serviced by a singleD-Module. As the storage adapter cooperates with the storage operatingsystem executing on the node to access information requested by theclients, the single D-Module may become overwhelmed with demand for dataaccess requests. The present invention overcomes the disadvantages ofthe previous striping systems by providing a technique that stripes datacontainers across volumes of a striped volume set (SVS) using one of aplurality of different data placement patterns to thereby reduce thepossibility of (cascading) hotspots arising due to each data containerusing the same data placement pattern within the SVS.

C. Storage Operating System

To facilitate access to the disks 130, the storage operating system 300implements a write-anywhere file system that cooperates with one or morevirtualization modules to “virtualize” the storage space provided bydisks 130. The file system logically organizes the information as ahierarchical structure of named data containers, such as directories andfiles on the disks. Each “on-disk” file may be implemented as set ofdisk blocks configured to store information, such as data, whereas thedirectory may be implemented as a specially formatted data container inwhich names and links to other data containers and directories arestored. The virtualization module(s) allow the file system to furtherlogically organize information as a hierarchical structure of datacontainers, such as blocks on the disks that are exported as namedlogical unit numbers (luns).

In the illustrative embodiment, the storage operating system ispreferably the NetApp® Data ONTAP®operating system available fromNetwork Appliance, Inc., Sunnyvale, Calif. that implements a WriteAnywhere File Layout (WAFL®) file system. However, it is expresslycontemplated that any appropriate storage operating system may beenhanced for use in accordance with the inventive principles describedherein. As such, where the term “Data ONTAP” is employed, it should betaken broadly to refer to any storage operating system that is otherwiseadaptable to the teachings of this invention.

FIG. 3 is a schematic block diagram of the storage operating system 300that may be advantageously used with the present invention. The storageoperating system comprises a series of software layers organized to forman integrated network protocol stack or, more generally, amulti-protocol engine 325 that provides data paths for clients to accessinformation stored on the node using block and file access protocols.The multi-protocol engine includes a media access layer 312 of networkdrivers (e.g., gigabit Ethernet drivers) that interfaces to networkprotocol layers, such as the IP layer 314 and its supporting transportmechanisms, the TCP layer 316 and the User Datagram Protocol (UDP) layer315. A file system protocol layer provides multi-protocol file accessand, to that end, includes support for the Direct Access File System(DAFS) protocol 318, the NFS protocol 320, the CIFS protocol 322 and theHypertext Transfer Protocol (HTTP) protocol 324. A VI layer 326implements the VI architecture to provide direct access transport (DAT)capabilities, such as RDMA, as required by the DAFS protocol 318. AniSCSI driver layer 328 provides block protocol access over the TCP/IPnetwork protocol layers, while a FC driver layer 330 receives andtransmits block access requests and responses to and from the node. TheFC and iSCSI drivers provide FC-specific and iSCSI-specific accesscontrol to the blocks and, thus, manage exports of luns to either iSCSIor FCP or, alternatively, to both iSCSI and FCP when accessing theblocks on the node 200.

In addition, the storage operating system includes a series of softwarelayers organized to form a storage server 365 that provides data pathsfor accessing information stored on the disks 130 of the node 200. Tothat end, the storage server 365 includes a file system module 360 incooperating relation with a volume striping module (VSM) 370, a RAIDsystem module 380 and a disk driver system module 390. The RAID system380 manages the storage and retrieval of information to and from thevolumes/disks in accordance with I/O operations, while the disk driversystem 390 implements a disk access protocol such as, e.g., the SCSIprotocol. The VSM 370 illustratively implements a striped volume set(SVS) utilizing the novel data placement technique of the presentinvention. As described further herein, the VSM cooperates with the filesystem 360 to enable storage server 365 to service a volume of the SVS.In particular, the VSM 370 implements the novel Locate( ) function 375to compute the location of data container content in the SVS volume tothereby ensure consistency of such content served by the cluster.

The file system 360 implements a virtualization system of the storageoperating system 300 through the interaction with one or morevirtualization modules illustratively embodied as, e.g., a virtual disk(vdisk) module (not shown) and a SCSI target module 335. The vdiskmodule enables access by administrative interfaces, such as a userinterface of a management framework 710 (see FIG. 7), in response to auser (system administrator) issuing commands to the node 200. The SCSItarget module 335 is generally disposed between the FC and iSCSI drivers328, 330 and the file system 360 to provide a translation layer of thevirtualization system between the block (lun) space and the file systemspace, where luns are represented as blocks.

The file system 360 is illustratively a message-based system thatprovides logical volume management capabilities for use in access to theinformation stored on the storage devices, such as disks. That is, inaddition to providing file system semantics, the file system 360provides functions normally associated with a volume manager. Thesefunctions include (i) aggregation of the disks, (ii) aggregation ofstorage bandwidth of the disks, and (iii) reliability guarantees, suchas mirroring and/or parity (RAID). The file system 360 illustrativelyimplements the WAFL file system (hereinafter generally the“write-anywhere file system”) having an on-disk format representationthat is block-based using, e.g., 4 kilobyte (KB) blocks and using indexnodes (“modes”) to identify data containers and data containerattributes (such as creation time, access permissions, size and blocklocation). The file system uses data containers to store meta-datadescribing the layout of its file system; these meta-data datacontainers include, among others, an mode data container. A datacontainer handle, i.e., an identifier that includes an mode number(inum), is used to retrieve an mode from disk.

Broadly stated, all modes of the write-anywhere file system areorganized into the mode data container. A file system (fs) info blockspecifies the layout of information in the file system and includes anmode of a data container that includes all other modes of the filesystem. Each logical volume (file system) has an fsinfo block that ispreferably stored at a fixed location within, e.g., a RAID group. Themode of the mode data container may directly reference (point to) datablocks of the mode data container or may reference indirect blocks ofthe mode data container that, in turn, reference data blocks of the modedata container. Within each data block of the mode data container areembedded modes, each of which may reference indirect blocks that, inturn, reference data blocks of a data container.

Operationally, a request from the client 180 is forwarded as a packetover the computer network 140 and onto the node 200 where it is receivedat the network adapter 225. A network driver (of layer 312 or layer 330)processes the packet and, if appropriate, passes it on to a networkprotocol and file access layer for additional processing prior toforwarding to the write-anywhere file system 360. Here, the file systemgenerates operations to load (retrieve) the requested data from disk 130if it is not resident “in core”, i.e., in memory 224. If the informationis not in memory, the file system 360 indexes into the mode datacontainer using the mode number (inum) to access an appropriate entryand retrieve a logical vbn. The file system then passes a messagestructure including the logical vbn to the RAID system 380; the logicalvbn is mapped to a disk identifier and disk block number (disk,dbn) andsent to an appropriate driver (e.g., SCSI) of the disk driver system390. The disk driver accesses the dbn from the specified disk 130 andloads the requested data block(s) in memory for processing by the node.Upon completion of the request, the node (and operating system) returnsa reply to the client 180 over the network 140.

It should be noted that the software “path” through the storageoperating system layers described above needed to perform data storageaccess for the client request received at the node may alternatively beimplemented in hardware. That is, in an alternate embodiment of theinvention, a storage access request data path may be implemented aslogic circuitry embodied within a field programmable gate array (FPGA)or an application specific integrated circuit (ASIC). This type ofhardware implementation increases the performance of the storage serviceprovided by node 200 in response to a request issued by client 180.Moreover, in another alternate embodiment of the invention, theprocessing elements of adapters 225, 228 may be configured to offloadsome or all of the packet processing and storage access operations,respectively, from processor 222, to thereby increase the performance ofthe storage service provided by the node. It is expressly contemplatedthat the various processes, architectures and procedures describedherein can be implemented in hardware, firmware or software. The presentinvention provides a system and method for providing a technique thatstripes data containers across volumes of a striped volume set (SVS)using one of a plurality of different data placement patterns to therebyreduce the possibility of (cascading) hotspots arising due to each datacontainer using the same data placement pattern within the SVS.

As used herein, the term “storage operating system” generally refers tothe computer-executable code operable on a computer to perform a storagefunction that manages data access and may, in the case of a node 200,implement data access semantics of a general purpose operating system.The storage operating system can also be implemented as a microkernel,an application program operating over a general-purpose operatingsystem, such as UNIX® or Windows NT®, or as a general-purpose operatingsystem with configurable functionality, which is configured for storageapplications as described herein.

In addition, it will be understood to those skilled in the art that theinvention described herein may apply to any type of special-purpose(e.g., file server, filer or storage serving appliance) orgeneral-purpose computer, including a standalone computer or portionthereof, embodied as or including a storage system. Moreover, theteachings of this invention can be adapted to a variety of storagesystem architectures including, but not limited to, a network-attachedstorage environment, a storage area network and disk assemblydirectly-attached to a client or host computer. The term “storagesystem” should therefore be taken broadly to include such arrangementsin addition to any subsystems configured to perform a storage functionand associated with other equipment or systems. It should be noted thatwhile this description is written in terms of a write any where filesystem, the teachings of the present invention may be utilized with anysuitable file system, including a write in place file system.

D. CF Protocol

In the illustrative embodiment, the storage server 365 is embodied asD-Module 350 of the storage operating system 300 to service one or morevolumes of array 120. In addition, the multi-protocol engine 325 isembodied as N-Module 310 to (i) perform protocol termination withrespect to a client issuing incoming data access request packets overthe network 140, as well as (ii) redirect those data access requests toany storage server 365 of the cluster 100. Moreover, the N-Module 310and D-Module 350 cooperate to provide a highly-scalable, distributedstorage system architecture of the cluster 100. To that end, each moduleincludes a cluster fabric (CF) interface module 340 a,b adapted toimplement intra-cluster communication among the modules, includingD-Module-to-D-Module communication for data container stripingoperations described herein.

The protocol layers, e.g., the NFS/CIFS layers and the iSCSI/FC layers,of the N-Module 310 function as protocol servers that translatefile-based and block based data access requests from clients into CFprotocol messages used for communication with the D-Module 350. That is,the N-Module servers convert the incoming data access requests into filesystem primitive operations (commands) that are embedded within CFmessages by the CF interface module 340 for transmission to theD-Modules 350 of the cluster 100. Notably, the CF interface modules 340cooperate to provide a single file system image across all D-Modules 350in the cluster 100. Thus, any network port of an N-Module that receivesa client request can access any data container within the single filesystem image located on any D-Module 350 of the cluster.

Further to the illustrative embodiment, the N-Module 310 and D-Module350 are implemented as separately-scheduled processes of storageoperating system 300; however, in an alternate embodiment, the modulesmay be implemented as pieces of code within a single operating systemprocess. Communication between an N-Module and D-Module is thusillustratively effected through the use of message passing between themodules although, in the case of remote communication between anN-Module and D-Module of different nodes, such message passing occursover the cluster switching fabric 150. A known message-passing mechanismprovided by the storage operating system to transfer information betweenmodules (processes) is the Inter Process Communication (IPC) mechanism.The protocol used with the IPC mechanism is illustratively a genericfile and/or block-based “agnostic” CF protocol that comprises acollection of methods/functions constituting a CF applicationprogramming interface (API). Examples of such an agnostic protocol arethe SpinFS and SpinNP protocols available from Network Appliance, Inc.The SpinFS protocol is described in the above-referenced U.S. PatentApplication Publication No. US 2002/0116593.

The CF interface module 340 implements the CF protocol for communicatingfile system commands among the modules of cluster 100. Communication isillustratively effected by the D-Module exposing the CF API to which anN-Module (or another D-Module) issues calls. To that end, the CFinterface module 340 is organized as a CF encoder and CF decoder. The CFencoder of, e.g., CF interface 340 a on N-Module 310 encapsulates a CFmessage as (i) a local procedure call (LPC) when communicating a filesystem command to a D-Module 350 residing on the same node 200 or (ii) aremote procedure call (RPC) when communicating the command to a D-Moduleresiding on a remote node of the cluster 100. In either case, the CFdecoder of CF interface 340 b on D-Module 350 de-encapsulates the CFmessage and processes the file system command.

FIG. 4 is a schematic block diagram illustrating the format of a CFmessage 400 in accordance with an embodiment of with the presentinvention. The CF message 400 is illustratively used for RPCcommunication over the switching fabric 150 between remote modules ofthe cluster 100; however, it should be understood that the term “CFmessage” may be used generally to refer to LPC and RPC communicationbetween modules of the cluster. The CF message 400 includes a mediaaccess layer 402, an IP layer 404, a UDP layer 406, a reliableconnection (RC) layer 408 and a CF protocol layer 410. As noted, the CFprotocol is a generic file system protocol that conveys file systemcommands related to operations contained within client requests toaccess data containers stored on the cluster 100; the CF protocol layer410 is that portion of message 400 that carries the file systemcommands. Illustratively, the CF protocol is datagram based and, assuch, involves transmission of messages or “envelopes” in a reliablemanner from a source (e.g., an N-Module 310) to a destination (e.g., aD-Module 350). The RC layer 408 implements a reliable transport protocolthat is adapted to process such envelopes in accordance with aconnectionless protocol, such as UDP 406.

A data container, e.g., a file, a block, or the like, is accessed in thefile system using a data container handle. FIG. 5 is a schematic blockdiagram illustrating the format of a data container handle 500 includinga SVS ID field 502, an mode number (inum) field 504, a unique-ifierfield 506, a striped flag field 508 and a striping epoch number field510. The SVS ID field 502 contains a global identifier (within thecluster 100) of the SVS within which the data container resides. Themode number field 504 contains an mode number of an mode (within an modedata container) pertaining to the data container. The unique-ifier field506 contains a monotonically increasing number that uniquely identifiesthe data container handle 500. The unique-ifier is particularly usefulin the case where an mode number has been deleted, reused and reassignedto a new data container. The unique-ifier distinguishes that reused modenumber in a particular data container from a potentially previous use ofthose fields. The striped flag field 508 is illustratively a Booleanvalue that identifies whether the data container is striped or not. Thestriping epoch number field 510 indicates the appropriate stripingtechnique for use with this data container for embodiments where the SVSutilizes differing striping techniques for different data containers.

E. File System Organization

In the illustrative embodiment, a data container is represented in thewrite-anywhere file system as an mode data structure adapted for storageon the disks 130. FIG. 6 is a schematic block diagram of an mode 600,which preferably includes a meta-data section 605 and a data section660. The information stored in the meta-data section 605 of each mode600 describes the data container (e.g., a file) and, as such, includesthe type (e.g., regular, directory, vdisk) 610 of data container, itssize 615, time stamps (e.g., access and/or modification time) 620 andownership, i.e., user identifier (UID 625) and group ID (GID 630), ofthe data container. The meta-data section 605 also includes a generationnumber 631, and a meta-data invalidation flag field 634, the latterindicating meta-data whether meta-data in the mode is usable. Thecontents of the data section 660 of each mode may be interpreteddifferently depending upon the type of data container (mode) definedwithin the type field 610. For example, the data section 660 of adirectory mode contains meta-data controlled by the file system, whereasthe data section of a regular mode contains file system data. In thislatter case, the data section 660 includes a representation of the dataassociated with the data container.

When an on-disk mode (or block) is loaded from disk 130 into memory 224,its corresponding in-core structure embeds the on-disk structure. Forexample, the dotted line surrounding the mode 600 indicates the in-corerepresentation of the on-disk mode structure. The in-core structure is ablock of memory that stores the on-disk structure plus additionalinformation needed to manage data in the memory (but not on disk). Theadditional information may include, e.g., a “dirty” bit 670. After datain the mode (or block) is updated/modified as instructed by, e.g., awrite operation, the modified data is marked “dirty” using the dirty bit670 so that the mode (block) can be subsequently “flushed” (stored) todisk. The in-core and on-disk format structures of the WAFL file system,including the modes and mode data container, are disclosed and describedin the previously incorporated U.S. Pat. No. 5,819,292 titled METHOD FORMAINTAINING CONSISTENT STATES OF A FILE SYSTEM AND FOR CREATINGUSER-ACCESSIBLE READ-ONLY COPIES OF A FILE SYSTEM by David Hitz et al.,issued on Oct. 6, 1998.

F. VLDB

FIG. 7 is a schematic block diagram illustrating a collection ofmanagement processes that execute as user mode applications 700 on thestorage operating system 300 to provide management of configurationinformation (i.e. management data) for the nodes of the cluster. To thatend, the management processes include a management framework process 710and a volume location database (VLDB) process 730, each utilizing a datareplication service (RDB 750) linked as a library. The managementframework 710 provides a user to an administrator 770 interface via acommand line interface (CLI) and/or a web-based graphical user interface(GUI). The management framework is illustratively based on aconventional common interface model (CIM) object manager that providesthe entity to which users/system administrators interact with a node 200in order to manage the cluster 100.

The VLDB 730 is a database process that tracks the locations of variousstorage components (e.g., SVSs, flexible volumes, aggregates, etc.)within the cluster 100 to thereby facilitate routing of requeststhroughout the cluster. In the illustrative embodiment, the N-Module 310of each node accesses a configuration table 235 that maps the SVS ID 502of a data container handle 500 to a D-Module 350 that “owns” (services)the data container within the cluster. The VLDB includes a plurality ofentries which, in turn, provide the contents of entries in theconfiguration table 235; among other things, these VLDB entries keeptrack of the locations of the flexible volumes (hereinafter generally“volumes”) and aggregates within the cluster. Examples of such VLDBentries include a VLDB volume entry 800 and a VLDB aggregate entry 900.

FIG. 8 is a schematic block diagram of an exemplary VLDB volume entry800. The entry 800 includes a volume ID field 805, an aggregate ID field810 and, in alternate embodiments, additional fields 815. The volume IDfield 805 contains an ID that identifies a volume used in a volumelocation process. The aggregate ID field 810 identifies the aggregatecontaining the volume identified by the volume ID field 805. Likewise,FIG. 9 is a schematic block diagram of an exemplary VLDB aggregate entry900. The entry 900 includes an aggregate ID field 905, a D-Module IDfield 910 and, in alternate embodiments, additional fields 1315. Theaggregate ID field 905 contains an ID of a particular aggregate in thecluster 100. The D-Module ID field 910 contains an ID of the D-Modulehosting the particular aggregate identified by the aggregate ID field905.

The VLDB illustratively implements a RPC interface, e.g., a Sun RPCinterface, which allows the N-Module 310 to query the VLDB 730. Whenencountering contents of a data container handle 500 that are not storedin its configuration table, the N-Module sends an RPC to the VLDBprocess. In response, the VLDB 730 returns to the N-Module theappropriate mapping information, including an ID of the D-Module thatowns the data container. The N-Module caches the information in itsconfiguration table 235 and uses the D-Module ID to forward the incomingrequest to the appropriate data container. All functions andinteractions between the N-Module 310 and D-Module 350 are coordinatedon a cluster-wide basis through the collection of management processesand the RDB library user mode applications 700.

To that end, the management processes have interfaces to (are closelycoupled to) RDB 750. The RDB comprises a library that provides apersistent object store (storing of objects) for the management dataprocessed by the management processes. Notably, the RDB 750 replicatesand synchronizes the management data object store access across allnodes 200 of the cluster 100 to thereby ensure that the RDB databaseimage is identical on all of the nodes 200. At system startup, each node200 records the status/state of its interfaces and IP addresses (thoseIP addresses it “owns”) into the RDB database.

G. Data Placement Technique to Avoid Cascaded Hotspots

The present invention overcomes the disadvantages of the prior art byproviding a technique that stripes data containers across volumes of astriped volume set (SVS) using one of a plurality of different dataplacement patterns to thereby reduce the possibility of hotspots arisingdue to each data container using the same data placement pattern withinthe SVS. Illustratively, the SVS is serviced by a storage systemarchitecture that comprises a plurality of nodes interconnected as acluster. Notably, the novel technique enables more than one dataplacement pattern to be used to stripe the data containers across thevolumes of the SVS, thus facilitating steady servicing of data accessrequests by the nodes and reducing the effects of hotspots.

Illustratively, the SVS is associated with a set of striping rules thatdefine a particular stripe algorithm, a stripe width and an ordered listof volumes within the SVS. The stripe algorithm specifies the manner inwhich data container content is apportioned as stripes across theplurality of volumes, while the stripe width specifies the size/width ofeach stripe. The ordered list of volumes specifies the function andimplementation of the various volumes and striping rules of the SVS. Forexample, the ordering of the volumes in the list may denote the mannerof implementing a particular data placement pattern.

Further, a Locate( ) function may be used to compute the location ofdata container content in the SVS to which a data access request isdirected to thereby ensure consistency of such content served by thecluster. Illustratively, the Locate( ) function accepts as an input anmode number of the data container and an offset value indicating anoffset into the data container. A first index value is determined byfirst adding the mode number to the value of the offset divided by thestripe width with the sum then taken modulo the striping table size.Next, an intermediate index value is generated by indexing the firstvalue into the ordered list of volumes. A hash value is then obtainedby, for example, indexing, using the mode number, into an arraycomprising values (numbers) that have been selected to be mutually primewith the size of a striping table and with the number of aggregates inthe stripe. The first index value may then be cached into aconfiguration table. A final value is determined by multiplying theintermediate index value by the hash value, modulo the number of volumesof the SVS. The final value is then used to identify and locate thevolume (and node servicing the volume) by indexing into the stripetable.

FIG. 10 is a schematic block diagram of an exemplary VLDB SVS entry 1000in accordance with an embodiment of the present invention. The VLDBentry 1000 includes a SVS ID field 1005 and one or more sets of stripingrules 1030. In alternate embodiments additional fields 1035 may beincluded. The SVS ID field 1005 contains the ID of a SVS which, inoperation, is specified in data container handle 500.

Each set of striping rules 1030 illustratively includes a stripe widthfield 1010, a stripe algorithm ID field 1015, an ordered list of volumesfield 1020 and, in alternate embodiments, additional fields 1025. Thestriping rules 1030 contain information for identifying the organizationof a SVS. For example, the stripe algorithm ID field 1015 identifies astriping algorithm used with the SVS. In the illustrative embodiment,multiple striping algorithms could be used with a SVS; accordingly,stripe algorithm ID is needed to identify which particular algorithm isutilized. Each striping algorithm, in turn, specifies the manner inwhich file content is apportioned as stripes across the plurality ofvolumes of the SVS. In accordance with an illustrative embodiment of thepresent invention described herein, the novel data placement techniquemay be identified by one of the multiple stripe algorithm IDs eventhough the data placement technique utilizes a plurality of dataplacement patterns. The stripe width field 1010 specifies the size/widthof each stripe. The ordered list of volumes field 1020 contains the IDsof the volumes comprising the SVS. In an illustrative embodiment, theordered list of volumes comprises a plurality of tuples, each comprisinga flexible volume ID and the aggregate ID storing the flexible volume.Moreover, the ordered list of volumes may specify the function andimplementation of the various volumes and striping rules of the SVS. Forexample, the ordering of volumes in the list may denote the manner ofimplementing a particular data placement pattern, e.g., round-robin.

According to yet another aspect of the invention, a Locate( ) function375 is provided that enables the VSM 370 and other modules (such asthose of N-Module 310) to locate a D-Module 350 and its associatedvolume of a SVS in order to service a data access request to a file. TheLocate( ) function takes as arguments, at least (i) a SVS ID 1005, (ii)an offset within the file, (iii) the mode number for the file and (iv) aset of striping rules 1030, and returns the volume on which that offsetbegins within the SVS. For example, assume a data access requestdirected to a file is issued by a client 180 and received at theN-Module 310 of a node 200, where it is parsed through themulti-protocol engine 325 to the appropriate protocol server of N-Module310.

To determine the location of a D-Module 350 to which to transmit a CFmessage 400, the N-Module 310 may first retrieve a SVS entry 1000 toacquire the striping rules 1030 (and list of volumes 1020) associatedwith the SVS. The N-Module 310 then executes the Locate( ) function 375to identify the appropriate volume (and D-Module) to which to direct anoperation. Thereafter, the N-Module may retrieve the appropriate VLDBvolume entry 800 to identify the aggregate containing the volume and theappropriate VLDB aggregate entry 900 to ultimately identify theappropriate D-Module 350. The protocol server of N-Module 310 thentransmits the CF message 400 to the D-Module 350.

FIG. 11 is a schematic block diagram illustrating the periodicsparseness of data container content stored on volumes A 1105, B 1110and C 1115 of SVS 1100 in accordance with an embodiment of the presentinvention. File content is periodically sparse according to the SVSstriping rules, which specify a striping algorithm (as indicated bystripe algorithm ID field 1015) and a size/width of each stripe (asindicated by stripe width field 1010). By sparse, it is meant that oneor more regions of the data container are not populated with data. Thesparse region may be used to, for example, maintain consistent offsetvalues when committing data from disk to memory. Note that, in theillustrative embodiment, a stripe width is selected to ensure that eachstripe may accommodate the actual data referenced by, e.g., an indirectblock of a file.

In accordance with an illustrative round robin striping algorithm,volume A 1105 contains a stripe of file content or data (D) 1120followed, in sequence, by two stripes of sparseness (S) 1122, 1124,another stripe of data (D) 1126 and two stripes of sparseness (S) 1128,1130. Volume B 1110, on the other hand, contains a stripe of sparseness(S) 1132 followed, in sequence, by a stripe of data (D) 1134, twostripes of sparseness (S) 1136, 1538, another stripe of data (D) 1140and a stripe of sparseness (S) 1142. Volume C 1115 continues the roundrobin striping pattern and, to that end, contains two stripes ofsparseness (S) 1144, 1146 followed, in sequence, by a stripe of data (D)1148, two stripes of sparseness (S) 1150, 1152 and another stripe ofdata (D) 1154. It should be noted that use of the round robin stripingtechnique is only exemplary.

FIG. 12 is a flowchart detailing the steps of a procedure 1200 forprocessing a data access request directed to a data container within aSVS in accordance with an embodiment of the present invention. Theprocedure 1200 begins in step 1205 and continues to step 1210 where anN-Module 310 receives a data access request directed to an SVS by, e.g.,a client 180 sending the data access request to node 200. In step 1300,described further below in reference to FIG. 13, the N-Module uses aLocate( ) function to identify the volume containing the desired data.

In step 1215, the N-Module accesses the VLDB to identify the D-Modulehosting the volume containing the desired data. To determine thelocation of a D-Module 350 to which to transmit a CF message 400, theN-Module 310 may first retrieve a SVS entry 1000 to acquire the stripingrules 1030 (and list of volumes 1020) associated with the SVS. TheN-Module 310 then executes a process, such as Locate( ) function 375, toidentify the appropriate volume to which to direct the request.

Thereafter, the N-Module 310 may retrieve the appropriate VLDB volumeentry 800 to identify the aggregate containing the volume and theappropriate VLDB aggregate entry 900 to ultimately identify theappropriate D-Module 350. Once the N-Module 310 identifies the volumecontaining the desired data, the procedure proceeds to step 1220 wherethe N-Module forwards the data access request (via a CF message 400) tothe D-Module 350. Upon receiving the data access request, the D-Moduleprocesses the data access request in step 1225. The procedure thencompletes in step 1230.

FIG. 13 is a flowchart detailing the steps of a procedure 1300 foridentifying a volume of an SVS containing desired data of a datacontainer in accordance with an illustrative embodiment of the presentinvention. Volume identification may be implemented as a Locate( )function, as described above. Procedure 1300 begins in step 1305 andcontinues to step 1310 where a first index value is generated.Illustratively, the Locate( ) function accepts as an input an modenumber (inum) of the data container and an offset value or file blocknumber (fbn) within the data container.

The first index value is generated by first adding the mode number tothe value of the offset divided by the stripe width with this sum takenmodulo the striping table size, e.g.First Index Value=[(inum+(offset/stripe_width))modulo StripingTableSize]In step 1315, an intermediate index value is generated, e.g.:Intermediate Index Value=[Striping_Table_Entry[First Index Value]]In step 1320, a hash value is then generated, for example, by mappingthe mode number into numbers that have been selected to be mutuallyprime with the size of the striping table and with the list of orderedvolumes. The N-Module 310 may illustratively cache the first index valuein its configuration table 235. In step 1325, the final index value isdetermined by multiplying the intermediate index value by the hashvalue, modulo the number of volumes of the SVS, e.g.:Final Index Value=[(Intermediate Index Value*Hash_Value) Modulo Numberof Volumes in SVS]In step 1330, the final value is then used to identify and locate thevolume by indexing into a list of ordered volumes 1020 where theD-Module ID 860 forwards the incoming request to the appropriate datacontainer. The procedure then completes in step 1335.

In another illustrative embodiment, different SVS traversal patterns maybe used for separate regions of a single data container. One advantageof this embodiment is that even if a single data container werereceiving all the I/O requests, a “bottleneck” could still be avoided.This may be illustratively accomplished by generating a second hashvalue in step 1320.

The foregoing description has been directed to particular embodiments ofthis invention. It will be apparent, however, that other variations andmodifications may be made to the described embodiments, with theattainment of some or all of their advantages. Specifically, it shouldbe noted that the principles of the present invention may be implementedin non-distributed data container systems. Furthermore, while thisdescription has been written in terms of N and D-Modules, the teachingsof the present invention are equally suitable to systems where thefunctionality of the N and D-Modules are implemented in a single system.Alternately, the functions of the N and D-Modules may be distributedamong any number of separate systems, wherein each system performs oneor more of the functions. Additionally, the procedures, processes and/ormodules described herein may be implemented in hardware, software,embodied as a computer-readable medium having program instructions,firmware, or a combination thereof. Therefore, it is the object of theappended claims to cover all such variations and modifications as comewithin the true spirit and scope of the invention.

What is claimed is:
 1. A system for striping a plurality of datacontainers across a striped volume set, comprising: a plurality of nodesinterconnected as a cluster, each node having a processor, a networkelement, and a data element; the network element of each node configuredto receive data access requests directed to a striped volume set, thenetwork element further configured to: use a locate function to identifya volume using an inode number and offset values indicating an offsetinto each data container for striping; use a volume location database toidentify the data element hosting the identified volume for each datacontainer; and forward the received data access requests to theidentified data element for each data container; and the identified dataelement configured to process a first data access request associatedwith a first data container using a first data placement pattern used tostripe the first data container across the striped volume set, whereinthe first data placement pattern is selected based on a first inodenumber associated with the first data container, the identified dataelement further configured to process a second data access requestassociated with a second data container using a second data placementpattern used to stripe the second data container across the stripedvolume set, wherein the second data placement pattern is based on asecond inode number associated with the second data container andwherein the second data placement pattern is different from the firstdata placement pattern.
 2. The system as defined in claim 1 wherein thefirst data placement pattern is used alternately with the second dataplacement pattern for striping into the first data container to reducehotspots arising due to each data container using a same data placementpattern.
 3. The system as defined in claim 1 wherein the first datacontainer and second data container comprise files.
 4. The system asdefined in claim 1 wherein the network element is further configured to:calculate a first value by adding the first inode number to a firstoffset value divided by a stripe width modulo a size of a stripingtable; calculate an intermediate value by indexing the first value intoan ordered list of volumes; calculate a hash value of an inodeassociated with the first data container by indexing, using the firstinode number, into an array having values that are selected to bemutually prime with a size of the ordered list of volumes; calculate afinal value by multiplying the intermediate value by the hash valuemodulo a number of volumes of the striped volume set; and index into thestriping table using the final value to identify and locate the volumethat provides a new location to commence striping the first datacontainer across the striped volume set wherein hotspotting is avoided.5. The system as defined in claim 1 wherein the first data placementpattern and the second data placement patterns are selected from a setof data placement patterns.
 6. The system as defined in claim 5 whereinthe set of data placement patterns contains an equal number of itemsused by a hash table to identify a selected data placement pattern. 7.The system as defined in claim 1 wherein the network element is furtherconfigured to associate the striped volume set with at least onestriping rule, and the at least one striping rule utilizing the firstinode number of the first data container, and at least one of a firstoffset value into the first data container, a number of volumes in thestriped volume set and an ordered set of volumes within the stripedvolume set to generate a hash value to identify the first data placementpattern.
 8. The system as defined in claim 7 wherein to generate thehash value further comprises using the first inode number of the firstdata container to index into a table containing available hash values.9. The system as defined in claim 8 wherein the first inode number andthe second inode number are mutually prime.
 10. A non-transitorycomputer readable medium containing executable program instructionsexecuted by a processor in a computer network configured as a cluster ofa plurality of nodes, comprising: program instructions that configure anetwork element of each node to receive data access requests directed toa striped volume set, program instructions that further configure thenetwork element to: use a locate function to identify a volume using aninode number and offset values into each data container for striping;use a volume location database to identify a data element hosting theidentified volume, of the striped volume set, for each data container;forward the received data access requests to the identified data elementfor each data container; process a first data access request using afirst data placement pattern used to stripe a first data containeracross the striped volume set, wherein the first data placement patternis selected based on a first inode number associated with the first datacontainer; and process a second data access request using a second dataplacement pattern used to stripe a second data container across thestriped volume set, wherein the second data placement pattern isselected based on a second inode number associated with the second datacontainer, and wherein the second data placement pattern is differentform the first data placement pattern so as to avoid hot spotting. 11.The computer readable medium of claim 10, wherein the programinstructions that configure the network element further comprise programinstructions that: calculate a first value by adding the first inodenumber to a first offset value associated with the first data container,divided by a stripe width modulo a size of a striping table; calculatean intermediate value by indexing the first value into an ordered listof volumes; calculate a hash value of an inode associated with the firstdata container by indexing, using the first inode number, into an arrayhaving values that are selected to be mutually prime with a size of theordered list of volumes; calculate a final value by multiplying theintermediate value by the hash value modulo a number of volumes of thestriped volume set; and index into a striping table using the finalvalue to identify and locate the volume that provides a new location tocommence striping the first data container across the striped volume setwherein hotspotting is avoided.
 12. The computer readable medium ofclaim 10 wherein the program instructions that configure the networkelement further comprise: program instructions that associate thestriped volume set with at least one striping rule that utilizes thefirst inode number of the first data container, a first offset valueinto the first data container, a number of volumes in the striped volumeset and an ordered set of volumes within the striped volume set togenerate a hash value to identify the first data placement pattern. 13.The computer readable medium of claim 10 wherein the first dataplacement pattern is used alternately with the second data placementpattern for striping into the first data container to reduce hotspotsarising due to each data container using a same data placement pattern.14. A method of striping a data container across a striped volume set,comprising: coupling a network element to a data element, of a nodehaving a processor, that serves data access requests for a stripedvolume set, the network element configured to associate a first datacontainer with a first data placement pattern, utilized to stripe thefirst data container across the striped volume set, based on a firstinode number associated with the first data container; configuring thenetwork element to further associate a second data container with asecond data placement pattern, utilized to stripe the second datacontainer across the striped volume set, based on a second inode numberassociated with the second data container, the second data placementpattern different from the first data placement pattern, wherein thefirst data placement pattern is used alternately with the second dataplacement pattern for striping into the first data container to reducehotspots arising due to each data container using a same data placementpattern.
 15. The method of striping a data container across a stripedvolume set as defined in claim 14 further comprising: configuring thestriped volume set with at least one striping rule, and the at least onestriping rule utilizes the first inode number of the first datacontainer, an offset value into the first data container, a number ofvolumes in the striped volume set and an ordered set of volumes withinthe striped volume set to generate a hash value to identify the firstdata placement pattern.
 16. The method of striping a data containeracross a striped volume set as defined in claim 15 further comprising:calculating a first value by adding the first inode number to saidoffset value divided by a stripe width modulo a size of a stripingtable; calculating an intermediate value by indexing the first valueinto an ordered list of volumes; calculating, a hash value of an inodeassociated with the first data container by indexing, using the firstinode number, into an array having values that are selected to bemutually prime with a size of the ordered list of volumes; calculating,by the processor, a final value by multiplying the intermediate value bythe hash value modulo a number of volumes of the striped volume set; andindexing into the striping table using the final value to identify andlocate a volume that provides a new location to commence striping thefirst data container across the striped volume set wherein hotspottingis avoided.